1. Field of the Invention
The present invention relates to a light-emitting diode (LED), and more particularly, to a white light LED component having a single LED chip and two kinds of phosphor.
2. Description of the Prior Art
Having the advantages of low power consumption, long lifespan (about ten times as long as that of an incandescent lamp), and, most importantly, high color rendering index (CRI) such that a white light LED (W-LED) component is capable of generating visible radiation that will not damage art, it has become one of the most popular illuminating devices in a competitive market demanding a high CRI.
An easy method for making a W-LED component is to combine a blue light LED chip capable of emitting blue light and a red light LED chip capable of emitting red light with a green light LED chip capable of emitting green light to form the W-LED component. The W-LED component is therefore capable of emitting white light, which is formed by mixing the blue light, the red light, and the green light.
However, the above three-in-one W-LED component is expensive, for it has to include three LED chips. Moreover, since the three LED chips each have a light-emitting efficiency different from one-another (The light-emitting efficiency of the blue LED chip is higher than the light-emitting efficiency of the red/green LED chip.), the white light emitted by the W-LED component, which is composed of the three LED chips, has a low CRI.
In order to overcome the above drawbacks, Nichia Chemical Co. disclosed a W-LED component consisting of a single LED chip and phosphor having a chemical formula of (Y1−p−q−rGdpCeqSmr)3(Al1−sGas)5O12 where p is between 0-0.8, q is between 0.003-0.2, r is between 0.0003-0.08, and s is between 0-1. The single LED chip is capable of emitting luminescent light. The phosphor is doped into epoxy resin used to cover the single LED chip. It is capable of absorbing luminescent light with predetermined wavelength, such as the luminescent light emitted by the single LED chip, and emitting an emission. As a result, the luminescent light emitted by the single LED chip, except the predetermined luminescent light, combines with the emission emitted by the phosphor to form white light.
The W-LED component disclosed by Nichia Chemical Co. comprises nothing but the single LED chip and photoluminescence phosphor; it is a mature and cheap product.
However, in addition to the phosphor having the chemical formula of (Y1−p−q−rGdpCeqSmr)3(Al1−sGas)5O12, a variety of phosphors can be used to be combined with the single LED chip to form a W-LED.
Moreover, in order to improve CRI, the prior art's W-LED component comprises another red phosphor CaS:Eu. The red phosphor CaS:Eu, which comprises an S-compound, lacks of stability. For example, the red phosphor CaS:Eu decomposes easily in humid and high temperature environments. As a result, a W-LED component having unstable red phosphor CaS:Eu has a poor CRI and a short lifespan.